The present invention is directed to improvements to medical diagnostic ultrasonic imaging systems that avoid the drawbacks associated with predetermined, stored front-end gains.
Medical diagnostic ultrasound imaging systems typically use preset front-end gains. In many applications multiple front-end gains are stored, and an appropriate front-end gain is selected for a particular application based upon the specific transducer and the transmit and receive frequencies in use for a given examination. Such stored front-end gains are often generated based on assumptions about the attenuation coefficient of the propagation medium. However, the attenuation coefficient can vary widely, depending upon the type of tissue being imaged. This is particularly true when a part of the propagation path passes through a non-attenuative structure, such as the bladder, the gall bladder, a cyst, amniotic fluid, or the like, or through blood pools (such as those encountered in chambers of the heart, the aorta, and other large vessels). In these cases, a preset front-end gain can be suboptimal.
Some prior-art ultrasonic imaging systems apply a portion of the user-controlled system gain, e.g. master gain and time gain compensation, to the front-end amplifier as an offset to a predetermined front-end gain curve. However, these systems often suffer from sub-optimal front-end gain, not only because the user gain controls are typically only range varying, but also because it is not easy to detect over-gain or under-gain conditions, except perhaps in extreme cases, and then only in B-mode imaging. Display dynamic range and post processing map selections, monitor brightness/contrast settings, and ambient light may prevent detection of over-gain and under-gain conditions. Even when extreme over-gain and under-gain conditions are present, user-controlled gain is often left misadjusted due to user inexperience, lack of sufficient time for continuous gain adjustments, subjective brightness preferences, and the like.
If the front-end gain is set too high for a particular application, the front-end amplifiers of the imaging system saturate. This can cause loss of resolution and, in the event of a high degree of saturation, loss of much or all of the imaging information.
On the other hand, if the front-end gain is set too low for a particular application, then the signal-to-noise ratio of the acquired receive signal is compromised. This loss in signal-to-noise ratio is due to the fact that there are typically noise sources such as AND quantization noise in the receive signal path after the front-end gain stage.
By way of introduction, one preferred embodiment described below adaptively sets the front-end gain of a medical diagnostic ultrasound imaging system by acquiring a plurality of receive samples that vary in range (or in range and azimuth), generating a gain function that varies in range (or in range and azimuth) as a function of envelope amplitude of the acquired receive samples, and then controls the front-end gain of the imaging system with the generated gain function. In this way, the front-end gain is consistently set to a high level that avoids saturation.
The foregoing discussion has been provided merely by way of introduction, and is not intended as a limitation on the following claims.